Visual display units (VDUs) are used to present information visually. Electronic VDUs include television sets and computer monitors for example. They receive information as electric signals and convert them for display as visual images on a screen.
Electronic display units, such as liquid crystal displays (LCDs), for example, may consist of pixels, which are discrete optical elements. The optical states of these elements change in response to an electrical potential (voltage) applied thereacross. The optical characteristics, such as the polarization thereof, scattering angle and reflectivity of each pixel depend upon these optical states. By providing voltage selectively to each pixel of the display, a visual image may be constructed and displayed.
Active optical elements such as liquid crystals, may deteriorate over time. Exposure to dampness and air within the environment may hasten this deterioration, particularly where the optical elements are susceptible to oxidation. Typically, the optical elements are protected from the environment by being sandwiched between two substrates. Depending upon the particular configuration, such substrates can include a number of functional layers such as glass or plastic panels, polarizers, alignment layers, color filters and electrodes. The electrodes, which provide an excitation voltage across the optical elements, are connected to an external power source via conductive pathways.
Connecting wires crossing the protective layer introduce leaky channels through which air seepage may occur, thereby hastening the deterioration of the optical elements.
A further cause of deterioration of visual displays is the excitation voltage itself which can cause some optical elements, such as liquid crystals, to be degraded by electrolysis. Much time and effort is devoted to finding cost effective solutions to overcome this problem. For example, in some systems the polarity of the excitation voltage is preconfigured to reverse periodically such that, over time, the net voltage across through the optical element is zero.
There is a need therefore for a visual display unit in which optical elements are protected against degradation from environmental influences and electrolysis. The present invention addresses this need.